This invention relates generally to anti-theft devices and more particularly concerns a locking nut which cannot be removed by conventional means for use in connecting separate pieces of oil field equipment.
Conventional oil field equipment, such as a christmas tree, is dangerously exposed to theft in ordinary use. A christmas tree includes various valves and other assemblies located at the top of a well bore on the surface of the earth. The christmas tree controls the flow of oil or gas from the well bore into collection means such as a pipeline network. The various valves and other pieces of equipment are conventionally joined by bolted flanges, which are integral parts of the valves and other equipment. The christmas trees are frequently located in remote areas and are not guarded or otherwise attended to by persons who could prevent their theft. In the past it has been a simple matter for a thief to close the bottommost valve and thereby isolate the well pressure from the remainder of the christmas tree. The thief then simply unbolts the remaining valves and assemblies of the christmas tree from the bottommost valve by removing the bolts or studs in the flanged connection immediately above the bottommost valve. If necessary for portability, other bolted flange connections of the christmas tree may also be unbolted, to reduce the weight of the individual pieces. On occasion, when well conditions permit, even the bottommost valve is unbolted and stolen in a similar fashion, leaving the well bore exposed to the environment at great risk to both the condition of the well and the environment.
A desirable way of reducing or eliminating the thefts of christmas trees is to join the flanged connections of the various valves and other pieces of equipment with means that cannot be removed by conventional means. Anti-theft bolts have been designed for or adapted to this purpose in the past as in U.S. Pat. No. 4,253,509, issued Mar. 3, 1981. It discloses a theft deterrent locking nut which includes a bolt, a round headed nut, and a locking insert which is threaded into the bolt and precludes the removal of the nut from the bolt. This device is being successfully used in the oil field to deter the theft of christmas trees and other equipment, as it is very difficult to remove by a potential thief. However, even though the device is removable by an authorized person, and reuseable, such as to repair or replace the equipment at the well head, it suffers from the disadvantage that it is very difficult to remove.
Other devices also used for theft deterrent purposes on oil field christmas trees include a larger version of the automobile wheel nut disclosed in U.S. Pat. No. 3,241,408, issued to McCauley on Mar. 22, 1977. This device is a single piece nut with a round exterior and a flat end with a groove routed into the end. A wrench having a complementary raised groove is engaged with the nut in order to turn it. Although the exterior shape of the nut makes it more difficult to engage than a conventional hex nut, this one piece nut has no internal mechanism to prevent it from being removed by simply rotating the nut.
Therefore it is an object of the invention to provide an anti-theft safety nut which is difficult for thieves to remove.
It is a further object of the invention to provide an anti-theft safety nut which positively engages with a bolt and cannot be disengaged therefrom by unauthorized persons.